Mineral fiber insulation is well known and has been a commercial product for an extended period of time. The insulation is typically made from rock or slag fibers often referred to as mineral wool or rock wool. The insulation is made from a calcium magnesium aluminum silicate glass. It is produced by melting a mixture of various slags and/or rock wool raw materials in a coke fired cupola. Alternatively, the raw materials can be melted in an electric or gas heated furnace. After the raw materials have been melted together, the wool is produced by either a multi-wheel centrifuge apparatus or by a Downey apparatus. Typically, if the fibers produced from this glass material are used as an insulation material, they are bound together by phenolic resins.
Previously in the art, insulation products were formed from asbestos fibers. Asbestos fibers, when inhaled, may cause disease in humans. Although the exact mechanism responsible for the biological activity of inhaled asbestos fibers is unknown, it is believed that their long residence time in the lung contributes to their ability to cause disease. Although mineral fibers have not been linked to disease in humans and their residence time in the human lung appears to be much shorter than that of asbestos fibers, it has become desirable to produce a mineral wool having an improved biosolubility.
One would expect that increasing the solubility of the mineral wool fibers would decrease the time the mineral wool fibers would remain in a human lung if they were inhaled. The dissolution rate of wool fibers in saline solutions similar to those existing in a human lung can be significantly increased by altering the chemical composition of the fiber, but there remains the problem of accomplishing this in such a way that other important properties of the mineral wool for commercial purposes are unimpaired.